Acoustic apparatus



Jan. 27, 1959 H. F. OLSON ETAL 2,870,856

ACOUSTIC APPARATUS Filed May 22, 1953 INI/ENTORS l! TTORNE Y United States Patent f) ACOUSTIC .APPARAlUS Harry Olson, Princeton, and John. l. Preston, Metedeconk, N. J., assignors toRadiaCorporation of America, a corporation.A of.Delaware;

Application May 22,v 1953, Serial No, 356,755V

3 Claims. (Cl: 18h-9.5)*A

This .invention yrelates to` v acoustic if apparatus and,vr more particularly, althoughv not necessarily exclusively, to` an improved type labyrinthal acoustic passage, or terminat-V ing device foruselwith pressure. responsive microphones,

The pressure operated portion ofpa milcrophoneshould theoretically be terminated inta ftubem, or pipe of ,infinite length,y butin practice ister-minated ina relatively long tube pacltjed with suitable` dampingumaterial, suchrfor example, as ozite.4 In thepast, therlabyrinthal acoustic passage or folded pipe for pressure responsive microphones has consisted, for the most part, of a sol id member or bodyhaving aplurality of 'longitudinally extending bores therethrough, vwhich are seriallyconnected together to provide a` single continuous passageway of ,relatively great length. This passageway isrgenerally filledk with suitable damping materialsuch, for example, as loosely packedhair felt or the like. The assembly of a structure as above described obviously requires great care in the manufacture thereof, so that the bores and mating passageways may be accurately located. No economy results from such an involved procedure. Further, in older type labyrinths much of the available space in the solid member or body was not utilized since large connecting sections or areas remained after the drilling operation to provide the bores, These remaining portions, resulted in a heavier overall structure and a more cumbersome microphone.

The primary object of the present invention is to provide a simple labyrinthal acoustic passage which utilizes the available space more efliciently.

More particularly, it is an object of the invention to provide an improved labyrinth structure which is simpler to manufacture.

Another object of the invention is to provide a labyrinthal acoustic passage for a microphone which may comprise a relatively simple two part unit providing an easier and more eiciently assembled and lighter weight device.

In accordance with the present invention, there is provided a substantially hollow cylindrical receptacle which is or may be closed at one end. An elongated paddle wheel or multiple iinned or vaned structure is provided for insertion within the receptacle. The vanes of the above-mentioned structure surround and radiate spokelike from a central core member. A central bore is or may be drilled along the longitudinal axis of the fmned structure and is provided with an undercut portion at one end thereof. A second bore is disposed adjacent and parallel to the rst bore. The second bore is also provided with an undercut portion at one end thereof. Alternate ones of the individual vanes or ns of the multiple vaned structure are undercut at the ends thereof. The vaned structure is adapted to be inserted and to tightly t within the receptacle. The space beween each one of the individual vanes or tins of the structure provides one passage of a series of interconnecting passages which form the diiferent air paths of a labyrinth or folded pipe.

2,870,856 Patented jan. 271959.

ICC

The novel features that are considered characteristic of the-invention are setforthwith particularity in the appended claims. Theinvention itself, however, both as toV its, organization and method of operation, as well as additional objects andadyantages, willA be bestunderstood from the following descriptionofseveral ernbloli-l mentsthereof, whenread in connection with the accom; panyingdrawing, in which:

Fig. l is an explodedperspective view ofV thel present invention; a

Fig. 2 isvianelevational view partially in section of a microphone utilizing thepresent'v invention;l

Fig. 3 isa perspective viertl ofthe llabyrinth illustrating the air paths therein;.and

Fig. 4 is ,anillustrativeshowing, ofa dillereutvmeans for terminating the labyrinth of Fig. "3.

Referring more particularly to the drawing, thereis shown,l inv Fig. l, alhollow; cylindrical member 10. The member-0isprOVdedWith two inner annular beveled lip or ledge portions 12 and 14. The two beveled edges 12 and 14 provide means for securing thecylinder 10 to the various associated parts now to be described.

The .elongatedstructure 16fis .provided with aplurality ofpilatradial; vanes or iins18'integral therewith; A centralylongitudinalrbore 20undercut at one end 21, as shown-` in Fig. 2, and an adjacent parallel outer bore 22 are. provided in the structure 16;. Alternate ones of the radialuns 18areundercutin|order to providea circuitous pathwayor labyrinth.Y Oneend portion 24 of an outer bQlt.22frisl,undercut. Thevstructure 16 is adaptedto be inserted and to tightly t within the cylindrical member 10.

A bottom member or end bell 26 may be provided for attachment to one end portion of the cylindrical member 10. The end bell 26 may consist of a domeshaped member having a top plate 28 disposed thereon or integral therewith. An opening 30 is provided in one portion of the top plate 28 for cooperation with the outer bore 22 in the structure 16. The end bell 26 is further provided with an annular lip or ledge 32. One lip 14 of the cylindrical member 10 is adapted to be seated on the ledge 32. The end bell 26 provides a simple and practical acoustical terminating means for the labyrinth. In order to provide a unitary assembly, the structure 16 is inserted within the cylindrical member 1t), as beforementioned. The lip 14 of the member 10 is pressed over the ledge 32 of the end bell 26 and suitably secured thereto. A labyrinthal acoustic passage 34 (Figs. 2 and 3) is thus provided. The labyrinth 34 is adapted to provide a relatively simply fabricated acoustical terminating device.

A sound translating unit 36 can be simply and etliciently secured to the labyrinthal acoustic passage 34 by fastening the edge or lip 12 on the cylindrical member 1G to a complementary annular groove or lip 38 on the sound translating unit 36, Fig. 2.

ln order to further simplify the fabrication of the labyrinth 34, the bottom bell 26 may be dispensed with. The cylindrical member 10 in this case is provided with an end plate 4) as shown in Fig. 4. The end plate 4t) may be integral with the cylindrical member 10.

The drawing of Fig. 3 illustrates, in schematic form the circuitous air-sound pathways through the labyrinth 34. Sound waves from the sound translating unit 345 enter the labyrinth 34 by way of the central bore 20 in the direction shown by the arrowhead 42. The sound waves travel longitudinally through the bore 20 until they are deflected by the top plate 28 of the end bell 26. The end portion of the central bore 20 is undercut at 2l, as shown in Fig. 2, so that the sound waves can be deflected into the parallel bore 22 and thus emerge from the bore 22 in the direction of the arrowheads 46. The bottom plate 37 of the sound translating unit 36 is adapted to deflect the sound waves causing them to follow the path parallel to the bore 22 buty in a reverse direction. Traversing the top of the structure 16 in a counter-clockwise direction, in the drawing of Fig. 3, there is shown a plurality of radial fins 48, 50, 52, 54, 56, 58, 60 and 62. Opposite ends of alternate fins are undercut as at 54 and 56, for example. Sound waves are caused 'to travel parallel to the fin 48 and are deflected by the top plate 28. Deflection by the top plate 28 reverses the direction of flow of the sound waves so that they travel parallel to n 50 in the direction of the arrowhead 64. At the end of their circuitous line of travel, the sound waves are finally shunted into the opening 30 in the end bell 26.

There has thus been described a novel labyrinthal acoustic passage which provides a more efficient use of space and which also provides a structure which is simpler to manufacture. The improved labyrinth, consisting of a flat vaned or paddle wheel structure which is slipped inside a cylinder to form the different paths of the labyrinth or folded pipe, is lighter in weight, thus lending itself to more extensive applications than older labyrinth devices.

What is claimed is:

1. A labyrinthal acoustic passage for cooperation with a microphone comprising a shell, an elongated member within said shell and extending longitudinally thereof, said elongated member having a plurality of fins radiating therefrom in radial array and extending therefrom to said shell, the surfaces of said finned member and said shell defining a plurality of longitudinally disposed, elongated air chambers within said shell, said chambers being enclosed along the length thereof, and means communicat- 4 ing with each of said air chambers to provide an enclosed, continuous passageway through said labyrinth.

2. A labyrinthal acoustic passage for cooperation with a microphone comprising a cylindrical shell, a cylindrical member Within said shell extending longitudinally thereof and having a plurality of longitudinally disposed fins radiating therefrom, Ythe side ends of said fins extending to said shell whereby said finned member and said shell define a plurality V'of longitudinally disposed air chamberswithin said shell, each of said chambers being enclosedV along the length thereof, and means communicating with the ends of adjacent ones of said chambers for providing a continuous passageway of great length through said shell.

3. A labyrinthal acoustic passage for cooperation with a microphone comprising a cylindrical shell, an elongated cylindrical member within said shell having a bore running longitudinally therethrough, said bore being concentric with said shell, a plurality of longitudinally disposed fins radially arranged on said member and extending therefrom to said shell, said finned member and said shell defining a plurality of air chambers radially disposed around said bore, means enclosing the ends of said cylindrical shell for providing passageways between the ends of adjacent ones of said chambers whereby an elongated, continuous passageway is provided, and means connecting said bore to a terminus of said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 874,676 Gulick Dec. 24, 1907 1,747,876 Metzgar Feb. 18, 1930 2,271,988 Olson Feb. 3, 1942 

